Valorization of agro-industry residues in the building and environmental sector: A review

Valorization of Manihot esculenta peel from environmental pollutant to sustainable engineering solutions for a cleaner future

As efforts intensify to address the environmental impact of agricultural waste, the valorization of Manihot esculenta peel (MEP) for sustainable engineering applications presents a unique opportunity to repurpose this class of agricultural waste to achieve environmental sustainability development goals while promoting socio-economic development of this pollutant. The inherent properties of MEP, such as its richness in carbohydrates and cellulose, make it a useful raw material for producing biofuels, bioethanols, biocomposites, and other sustainable engineering materials. Its resilience to adverse environmental conditions also makes MEP well-suited for cultivation in diverse agroecological settings, further enhancing its appeal as a sustainable resource. While existing review articles provide valuable insights into Manihot esculenta peel utilization across various industries, they often overlook the comprehensive valorization of Manihot esculenta for sustainable engineering applications, creating a notable knowledge gap. Through a systematic examination of innovative approaches documented in the literature, this research seeks to bridge this gap by elucidating strategies for repurposing cassava waste into valuable engineering materials to mitigate environmental pollution and promote sustainable resource utilization. By synthesizing existing research and identifying key research gaps, this study advances the understanding of Manihot esculenta peel's potential as a sustainable material and facilitates the transition toward greener engineering practices.

Effective biosorption of Al ions from drinking water by lignocellulosic biomass rice straw

High concentration of aluminum (Al) in drinking water is a major intake source of it and can result in serious diseases. Rice straw (RS) as lignocellulosic biomasses has great potential to peak up metal ions from aqueous environment, however, feasibility of Al3+ removal by RS has not been investigated yet. The present study aimed to evaluate the capacity of RS as a novel biosorbent for Al3+ from drinking water. Biosorption characteristics of RS were surveyed through several biological and physiochemical techniques. Additionally, isotherm, kinetic and thermodynamic studies were evaluated using various common models. BET profiles revealed the presence of textural mesoporosity on heterogeneous surface, which leading to improve the biosorption capacity. SEM-EDS analysis confirmed the morphological changes as irregularly particles of Al3+ on external surface via physical mechanism. The results of bioassays and FTIR analysis showed carboxylic and hydroxyl groups in lignin and pectin as the main Al3+ binding site. The batch experimental results showed the maximum biosorption capacity of 283.09 mg/g and removal efficiency of 94.86% for Al3+ at biosorbent dosage of 0.05 g/100 mL, contact time of 50 min, pH 7.5, and temperature of 30 °C. The Freundlich model has the best match and suggests the biosorption process as a multi-layer. According to the results of free activation energy, biosorption process was also physical. As thermodynamic result, the biosorption behavior was found spontaneous and endothermic. Consequently, results showed RS as an economical biosorbent for reducing Al3+ of drinking water. Meanwhile, it can be considered as one of the most appropriate methods for management of rice paddies waste.

Circular economy in the valorisation of food and other biowaste: case studies in small and medium-sized enterprises in the Belgian construction sector

The construction sector has significant impacts on the environment due to the consumption of resources and the production of waste. The implementation of circular economy strategies can improve the environmental performance of the sector, optimising the current production and consumption patterns, slowing and closing material loops, and using waste as a source of raw materials. Biowaste represents a key waste flow at the European scale. However, research on its application in the construction sector is still limited and product-oriented, with little insights into the processes of valorisation undertaken at the company's level. This study presents eleven case studies of Belgian small and medium-sized enterprises involved in biowaste valorisation in the construction sector in order to tackle this research gap in the Belgian context. Semi-structured interviews were conducted to identify the enterprise's business profile and its current marketing practices, as well as to analyse opportunities and barriers for market expansion and highlight current research interests. Results show that the overall picture is extremely heterogeneous in terms of sourcing, production methods, and products, while the barriers and success factors that have been identified are recurrent. This study contributes to the circular economy research in the construction sector by providing insights into innovative waste-based materials and business models.

Sustainable and circular agro-environmental practices: A review of the management of agricultural waste biomass in Spain and the Czech Republic

Sustainable and circular production models, such as the circular economy and circular bioeconomy, have become key mechanisms to leave behind the traditional linear model of food production. Under this approach and considering the waste biomass potential available in Spain and the Czech Republic, the main objective of this study is to analyse the most relevant aspects of the generation, use and regulation of agricultural waste biomass (AWB) in both countries. For this purpose, a scientometric analysis and systematic review of published research in the Scopus database were carried out. A complementary analysis of AWB management policies and regulations was also part of the methodology. The results show that Spain has published almost twice as much research as the Czech Republic. Furthermore, 91% of the retrieved research prioritizes the characterization and estimation of the potential of more than 15 AWB types. Among the main ones are olive residues, horticultural residues and wheat straw, which are used for producing organic amendments, bioenergy and biofuels. The results confirm that the reduction and valorization of AWB is an issue that has become more important in the last 13 years, mainly due to the policies and strategies for circular economy and circular bioeconomy. With this in mind, this study provides relevant information for governments on the aspects that need to be improved to advance in the valorization of AWB. This study also provides guidance to farmers on the reduction and/or recovery alternatives that they can implement to move towards sustainable and circular agriculture.

Valorization of biowastes for clean energy production, environmental depollution and soil fertility

The mother earth is a source of natural resources that, in conjunction with anthropogenic activities, generates a wide spectrum of different biowastes. These biomaterials can be used as low-cost raw feedstock to produce bioenergy, value-added products, and other commodities. However, the improper management and disposal of these biowastes can generate relevant environmental impacts. Consequently, it is imperative to explore alternative technologies for the valorization and exploitation of these wastes to obtain benefits for the society. This review covers different aspects related to valorization of biowastes and their applications in water pollution, soil fertility and green energy generation. The classification and characteristics of different biowastes (biosolids, animal wastes and effluents, plant biomass, wood and green wastes) including their main generation sources are discussed. Different technologies (e.g., pyrolysis, hydrothermal carbonization, anaerobic digestion, gasification, biodrying) for the transformation and valorization of these residues are also analyzed. The application of biowastes in soil fertility, environmental pollution and energy production are described and illustrative examples are provided. Finally, the challenges related to implement low-cost and sustainable biowaste management strategies are highlighted. It was concluded that reliable simulation studies are required to optimize all the logistic stages of management chain of these residues considering the constraints generated from the economic, environmental and social aspects of the biowaste generation sources and their locations. The recollection and sorting of biowastes are key parameters to minimize the costs associated to their management and valorization. Also, the concepts of Industry 4.0 can contribute to achieve a successful commercial production of the value-added products obtained from the biowaste valorization. Overall, this review provides a general outlook of biowaste management and its valorization in the current context of circular economy.

Environmental implications of reprocessing agricultural waste into animal food: An experience with rice straw and citrus pruning waste

The aim of this study is to conduct an environmental comparison, by applying the life cycle assessment (LCA) methodology, of two different compositions for animal foods each with two different nutritional contents ('high' for the lactation period, and 'low' for the rest of the year). Thus, for each nutritional content, the environmental performance of producing animal feed with a traditional composition mainly based on cereals is compared with a composition based on a mixture of biomass obtained from rice straw and citrus pruning waste. It was observed that the reprocessing of rice straw and citrus pruning waste into animal feed offered environmental potential compared to the current alternative of being burned in the fields. The environmental impact category global warming is especially improved, with impact reductions of up to 50% and 95%, respectively, for high and low nutritional content compositions. In addition, the alternatives proposed herein make it possible to avoid all the inconvenience and impacts on the health of the population living near the fields.

Eco-friendly particleboard production from coconut waste valorization

Reusing agro-industrial waste does not only help to mitigate environmental impact but also enables valorization through the development of new products. The aim is to enhance the physical and mechanical properties of particleboard panels produced with Eucalyptus wood and different proportions of waste products-coconut fiber (Cocos nucifera L.). Physical properties (density, water absorption, and thickness swelling) and mechanical properties (static bending and internal bond resistance) were assessed, and panels reinforced with coconut fiber showed the best qualities with higher density, greater dimensional stability, and less water absorption. Static bending resistance and internal bond resistance also increased significantly. This demonstrated the potential of achieving compatible characteristics for civil construction and furniture production through the inclusion of waste material. The impact of this research is obtained from the utilization of an important agro-industrial residue in the manufacture of permanent composites.

Calcium-pyro-hydrochar derived from the spent mushroom substrate as a functional sorbent of Pb2+ and Cd2+ from aqueous solutions

A calcium-pyro-hydrochar (Ca-PHC) can be distinguished as a novel sorbent of Pb²⁺ and Cd²⁺ from an aqueous solution. It was obtained using hydrothermal treatment of the spent mushroom substrate (SMS), followed by a CaCl₂·5H₂O activation and pyrolysis. The characterisation of chars before and after modifications was done by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) and Fourier transform infrared (FTIR). Batch experiments were performed to examine Ca-PHC's sorption properties and binding mechanisms to selected metal ions. The maximum sorption capacities of Ca-PHC for Pb²⁺ and Cd²⁺ were 297 mg g^-1, and 131 mg g^-1, respectively. The obtained results demonstrated that the sorption of Pb²⁺ and Cd²⁺ by Ca-PHC follows a pseudo-second kinetic model and Freundlich isotherm. The binding of the selected metals onto Ca-PHC was enabled by the ion-exchange mechanism, surface complexation, mineral precipitation and cation-π interaction. Thermodynamic parameters indicate that metal ions binding by Ca-PHC are spontaneous and endothermic. Due to the high adsorption capacities, the obtained Ca-PHC has good potential for application in industrial wastewater treatment. In addition, the demonstrated use of SMS highlights another possibility of applying this specific biomass relevant to sustainable and economical waste management in the growing mushroom industry.

A holistic overview on corn cob biochar: A mini-review

Corn cob is one of the agricultural waste materials subjected to improper burning, which creates pollution. It can be used for the production of green technologies for further applications. Carbonisation or slow pyrolysis could be promising alternative to burning. It has many applications, such as soil ameliorant, waste water treatment, carbon sequestration, composting, supercapacitor, fuel cell and biocomposites material. It motivated to investigate the suitability of corn cob as a potential material for biochar production and its application. The advanced form of analysis, such as thermogravimetric, scanning electron microscopy, surface area, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and Raman spectroscopy, is elaborated for in-depth knowledge of characteristics. The hypothesis is that if the available corn cob is used for biochar production, it will reduce the carbon dioxide (CO₂) emission. On a global level, conversion of available corn cob into biochar is expected to reduce CO₂ emission by 0.13 Gt per year. The reduction in CO₂ emission also favours economy. If 1 tonne of biomass per year is converted into biochar, 0.82 tonnes of CO₂ can be reduced per year and by considering the emission cost of Rs 1800 per tonne, the cost saving would be Rs 1476 per year. The presented mini-review article provides an outline of the state-of-art information on corn cob biochar and its novel application. It will be helpful to scientific domain to find new opportunities in biochar research and also the humanity will be benefitted due to reduction in greenhouse gases.

Rice Industry By-Products as Adsorbent Materials for Removing Fluoride and Arsenic from Drinking Water—A Review

In drinking water, high concentrations of fluoride and arsenic can have adverse effects on human health. Waste deriving from the rice industry (rice husk, rice straw, rice bran) can be promising adsorbent materials, because they are (i) produced in large quantities in many parts of the world, (ii) recoverable in a circular economy perspective, (iii) at low cost if compared to expensive conventional activated carbon, and (iv) easily manageable even in developing countries. For the removal of fluoride, rice husk and rice straw allowed to obtain adsorption capacities in the range of 7.9–15.2 mg/g. Using rice husk for arsenic adsorption, excellent results were achieved with adsorption capacities above 19 mg/g. The best results both for fluorides and arsenic (>50 mg/g) were found with metal- or chemical-modified rice straw and rice husk. Identifying the next steps of future research to ensure the upscaling of biochar from recovered by-products, it is fundamental to perform: (i) tests on real waters for multicomponent adsorption; (ii) experiments with pilot plants in continuous operation; (iii) cost analysis/real applicability of modification treatments such as metal coupling or chemical synthesis; (iv) more studies on the biochar stability and on its regeneration or recovery after use.

The use of urban biowaste and excavated soil in the construction sector: A literature review

Soil has been used as building material for thousands of years with a decrease in popularity after the industrial revolution. Nowadays, there is a growing interest in the implementation of unfired soil-based building solutions for their low environmental impact, performances and availability. Traditional soil construction techniques have recurrently included vegetal fibres to enhance soil performance and recent studies highlight a predominant use of agro- and non-agro-waste for unfired soil construction. The article reviews the state-of-the-art of the use of excavated soil and biowaste in the construction industry including a novel focus on urban-only waste and on building technologies using the integration of these two secondary construction material flows. Our literature review highlights a lack of references about the joint use of these secondary resources. Finally, future research orientations are suggested to promote their implementation in the building sector, which could improve urban waste management.

Comparative Life Cycle Assessment of lightweight Aggregates Made from Waste—Applying the Circular Economy

The application of Life Cycle Assessment in the construction sector can be a very useful tool to reduce the environmental impact generated by the sector. In order to quantify the improvement in environmental terms with the use of artificial lightweight aggregates (LWA) manufactured with waste, in this work, we conducted a comparative evaluation of the life cycle of LWAs for a total of five different scenarios: LWAs obtained in a traditional way, i.e., using exclusively clay in their manufacture (Spanish blond clay, Portuguese red clay and Portuguese blond clay), and LWAs manufactured with four different wastes, with a partial substitution of 2.5% for each of the clays per waste (almond and hazelnut shells, sludge from the purification of paper money, cork dust and coffee grounds). The functional unit was set as the production of 1 kilo of lightweight aggregates and the CML 2000 methodology and the SimaPro software were used. The results obtained in this research allow us to conclude that the addition of organic wastes showed a slightly higher environmental performance than the conventional system, the ALAs manufactured with almond and hazelnut shells being the most environmentally friendly option, with reductions of more than 30% in some cases, followed by the LWAs manufactured with coffee grounds. On the other hand, the addition of paper sewage sludge and cork dust represents minimal environmental optimization.

Sustainability Assessment of Solid Biofuels from Agro-Industrial Residues Case of Sugarcane Bagasse in a Mexican Sugar Mill

Motivated by the environmentally driven energy transition we live in, the valorization of biomass residues from the agro-industry as renewable energy can play an essential role in GHG emissions mitigation. To overcome the debate on the production and use of solid biofuels (SBF), in this study, we apply an integrated multicriteria tool for the assessment of the sustainability use of agro-industrial residues (AIR) as solid biofuels. Mexico has a vast AIR production, but frequently, the AIR are considered waste biomass. Still, when valorized, SBF do not have adverse effects on soil quality, are not responsible for biodiversity loss, and compete against food production as first-generation SBF. Nevertheless, the AIR present other environmental, social, and economic impacts that have not been adequately evaluated; therefore, we identified the need for a sustainability assessment of energy systems based on the use of SBF–AIR as input fuels. After reviewing previous work on sustainability assessment methodologies, multicriteria decision analysis methods, and indicator weighting methods, we considered it appropriate for this problem to apply a tool that integrates the entropic indicator weighting method into the discrete multicriteria decision analysis method called PROMETHEE. In terms of selected sustainability indicators, this tool was used to assess four electric energy supply systems of a Mexican sugar mill as a case study: current bagasse cogeneration, efficient bagasse cogeneration, a power generation system fueled only with fuel oil, and grid electricity only. Finally, after evaluating the mentioned energy systems with four sustainability indicators: GHG emissions, PM emissions, employments per energy unit (JOBS), and the net present value (NPV) of each alternative, we found the net outranking flow of the efficient bagasse system (EBS). which is the most sustainable system because it has the highest outranking flow value from the four considered alternatives, since it has the lower GHG emissions, reducing the current bagasse GHG emissions by 55% and the PM emissions by 58%. The EBS also shows the highest NPV system due to surplus electricity sales, resulting in the most profitable energy system analyzed.

Photoelectrocatalysis on TiO2 meshes: different applications in the integrated urban water management

Recently, among AOPs, photoelectrocatalysis (PEC) on TiO2 is gaining interest. In this study, five different real waters sampled in four different points of the integrated urban water management (IUWM) system were tested with PEC and UV alone, for comparison. This work aims to verify the effect of the PEC suggesting the optimal position in IUWM system where the PEC should be located to obtain the best performance. In groundwaters (GWs), PEC effectively removed atrazine-based compounds (> 99%), trichloroethylene, and perchloroethylene (96%), after 15 min of reaction time. However, given the low concentrations of emerging compounds, the synergistic effect of UV radiation with the catalyst and with the polarization of the mesh was not visible, with very few differences compared with the results obtained with UV alone. Pharmaceutical industrial wastewater (IWW) showed a significant increase in biodegradability after 2 h, both if subjected to PEC or UV (200%), despite the absence of COD removal. The PEC applied on IWW from a sewage sludge treatment plant allowed to effectively remove the COD (39.6%) and increase the biodegradability (300%). Good results in terms of COD removal (33.9%) and biodegradability increase (+900%) were also achieved testing PEC on wastewater treatment plant effluent. Except for GWs, PEC allowed significant EEO savings respect to UV alone (76.2-99.1%).

Comprehensive and critical appraisal of plant-based defluoridation from environmental matrices

Fluoride is recognized as one of the global environmental threats because of its non-biodegradable nature and long-term persistence in the environment. This has created the dire need to explore various defluoridation techniques (membrane process, adsorption, precipitation, reverse osmosis, ion exchange, and electrocoagulation). Owing to their cost ineffectiveness and high operational costs, these technologies failed to find any practical utility in fluoride remediation. Comparatively, defluoridation techniques involving the use of low-cost plant-derived adsorbents and fluoride phytoremediators are considered better alternatives. Through this review, an attempt has been made to critically synthesize information about various plant-based bioadsorbents and hyperaccumulators from existing literature. Moreover, mechanisms underlying the fluoride adsorption and accumulation by plants have been thoroughly discussed that will invigorate the researchers to develop novel ideas about process/product modifications to further enhance the removal potential of the adsorbents and plants. Literature survey unravels that various low-cost plant-derived adsorbents have shown their efficacy in defluoridation, yet there is an urgent need to explore their pragmatic application on a commercial scale.

Coconut shell ash enhances short-chain fatty acids production from anaerobic algae fermentation

This study proposed a novel method to enhance short-chain fatty acids (SCFAs) production from anaerobic algae fermentation by using coconut shell ash. The maximum SCFAs production was 683.0 mg COD/g VS at the ash dosage of 1.2 g/g TS, which was about 1.4-folds that of the control, and the enhancement of acetate production was the main path for the promotion of SCFAs. Coconut shell ash increased the pH and alkalinity of digestate, thereby reducing the use of alkaline reagents and being more resistant to acidic environments. Coconut shell ash promoted the processes of solubilization, hydrolysis and acetogenesis, and enriched hydrolytic microorganisms (e.g., Candidatus Microthrix) and acidifying microorganisms with acetate as substrate (e.g., Caldilinea and Proteiniphilum). Anaerobic fermentation residue with ash containing inorganic elements has the potential to be used as fertilizer, making this waste-control-waste strategy with more economic and environmental benefits for potential practical applications.

Enhancement of Methanogenic Activity in Volumetrically Undersized Reactor by Mesophilic Co-Digestion of Sewage Sludge and Aqueous Residue

To date, energy recovery from biological sewage sludge (BSS) by anaerobic digestion has been very popular. However, it can often happen that anaerobic reactors are volumetrically undersized, thus reducing performance in terms of biogas production. A continuous-flow pilot-scale plant was used to investigate, for the first time, the effects of mesophilic anaerobic co-digestion (MACoD) of sewage sludge and aqueous residue (AR) from a biosolids treatment plant (BTP) on methanogenic activity under low hydraulic retention time (HRT) conditions (to simulate the undersizing of the reactor). The results showed that the digestate is always more rapidly biodegradable than the matrices fed, while particulate COD hydrolyzed (12 ± 1.3%) is independent of the quantity of AR dosed. Feeding over 35% of soluble OLR, the total VFAs in the system strongly decreased, despite the low HRT. In correspondence with higher dosages of AR, the percentage of CH4 increased up to 77–78% and the CO2 CH4−1 ratio decreased to 0.25 ± 0.2. Specific methane production increased from 0.09 ± 0.01 m3CH4 kgCODremoved−1 with BSS alone to 0.28 ± 0.01 m3CH4CH4 kgCODremoved−1 in the case of BSS co-digested with AR. Moreover, co-digestion with AR from a BTP allowed continuous specific methanogenic activity to be enhanced from 1.76 ± 0.02 m3CH4 tVSS−1 d−1 to 6.48 ± 0.88 m3CH4 tVSS−1 d−1. Therefore, the MACoD of BSS and AR from a BTP could be a good solution to enhance methanogenic activity in a volumetrically undersized anaerobic digester with reduced HRT.

Extraction and Purification of Phosphorus from the Ashes of Incinerated Biological Sewage Sludge

Phosphorus depletion represents a significant problem. Ash of incinerated biological sewage sludge (BSS) contains P, but the presence of heavy metals (e.g., Fe and Al) is the main issue. Based on chemical characterization by SEM-EDS, ED-XRF and ICP-OES techniques, the characteristics and P content of bottom ash (BA) and fly ash (FA) of incinerated BSS were very similar. On BA, P extraction carried out in counter- current with an S:L ratio of 1:10 and H2SO4 0.5 M led to better extraction yields than those of a similar test with H2SO4 1 M and an S:L ratio of 1:5 (93% vs. 86%). Comparing yields with H2SO4 0.5 M (S:L ratio of 1:10), the counter-current method gave better results than those of the crossflow method (93% vs. 83.9%), also improving the performance obtained with HCl in crossflow (93% vs. 89.3%). The results suggest that the purification of the acid extract from heavy metals with pH variation was impractical due to metal precipitation as phosphates. Extraction with H2SO4 and subsequent treatment with isoamyl alcohol represented the best option to extract and purify P, leading to 81% extraction yields of P with low amounts of metals.

Development and Characterization of Rice Husk and Recycled Polypropylene Composite Filaments for 3D Printing

Nowadays the use of natural fiber composites has gained significant interest due to their low density, high availability, and low cost. The present study explores the development of sustainable 3D printing filaments based on rice husk (RH), an agricultural residue, and recycled polypropylene (rPP) and the influence of fiber weight ratio on physical, thermal, mechanical, and morphological properties of 3D printing parts. Thermogravimetric analysis revealed that the composite's degradation process started earlier than for the neat rPP due to the lignocellulosic fiber components. Mechanical tests showed that tensile strength increased when using a raster angle of 0° than specimens printed at 90°, due to the weaker inter-layer bonding compared to in-layer. Furthermore, inter layer bonding tensile strength was similar for all tested materials. Scanning electron microscope (SEM) images revealed the limited interaction between the untreated fiber and matrix, which led to reduced tensile properties. However, during the printing process, composites presented lower warping than printed neat rPP. Thus, 3D printable ecofriendly natural fiber composite filaments with low density and low cost can be developed and used for 3D printing applications, contributing to reduce the impact of plastic and agricultural waste.

Integrated Efforts for the Valorization of Sweet Potato By-Products within a Circular Economy Concept: Biocomposites for Packaging Applications Close the Loop

With the aim to fully exploit the by-products obtained after the industrial extraction of starch from sweet potatoes, a cascading approach was developed to extract high-value molecules, such as proteins and pectins, and to valorize the solid fraction, rich in starch and fibrous components. This fraction was used to prepare new biocomposites designed for food packaging applications. The sweet potato residue was added to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in various amounts up to 40 wt % by melt mixing, without any previous treatment. The composites are semicrystalline materials, characterized by thermal stability up to 260 °C. For the composites containing up to 10 wt % of residue, the tensile strength remains over 30 MPa and the strain stays over 3.2%. A homogeneous dispersion of the sweet potato waste into the bio-polymeric matrix was achieved but, despite the presence of hydrogen bond interactions between the components, a poor interfacial adhesion was detected. Considering the significant percentage of sweet potato waste used, the biocomposites obtained show a low economic and environmental impact, resulting in an interesting bio-alternative to the materials commonly used in the packaging industry. Thus, according to the principles of a circular economy, the preparation of the biocomposites closes the loop of the complete valorization of sweet potato products and by-products.

Selection Criteria for Building Materials and Components in Line with the Circular Economy Principles in the Built Environment—A Review of Current Trends

A growing concern is given to the environmental impacts caused by the construction industry. Waste generation, resource consumption, and greenhouse gas emissions are the main drawbacks of the rapid urbanization that the world is witnessing. As a response to these pressing issues, policymakers and academia are exploring the concept of Circular Economy (CE) to manage resources better and achieve resource efficiency while eliminating waste. One of the strategies to implement CE in the built environment is to select the appropriate building materials and components from the early stages to carry out the concept’s principles along the value chain and create a closed-loop system. Therefore, this study aims at identifying selection criteria for building elements according to CE principles through a review of the latest research. Results have shown that little has been concretely achieved in terms of a paradigm shift to CE since the main focus of the literature is still the use of recycled products and the recyclability of building materials and components at their end-of-life. Although the present study is solely focused on the technical aspect of building materials and components, it outlines current adopted criteria to bring about a circular built environment and highlights the need for a more innovative approach to attain higher circularity levels.

Unravelling the Environmental Application of Biochar as Low-Cost Biosorbent: A Review

In this age, a key target for enhancing the competitiveness of the chemical, environmental and biotechnology industries is to manufacture high-value products more efficiently and especially with significantly reduced environmental impact. Under this premise, the conversion of biomass waste to a high-value added product, biochar, is an interesting approach under the circular economy principles. Thus, the improvements in the biochar production and its new and innovative uses are hot points of interest, which are the focus of vast efforts of the scientific community. Biochar has been recognized as a material of great potential, and its use as an adsorbent is becoming a reliable strategy for the removal of pollutants of different streams, according to its high adsorption capacity and potential to eliminate recalcitrant compounds. In this review, a succinct overview of current actions developed to improve the adsorption capability of biochar, mainly of heavy metal and organic pollutants (dyes, pharmaceuticals and personal care products), is summarized and discussed, and the principal adsorption mechanisms are described. The feedstock and the production procedure are revealed as key factors that provide the appropriate physicochemical characteristics for the good performance of biochar as an adsorbent. In addition, the modification of the biochar by the different described approaches proved their feasibility and became a good strategy for the design of selective adsorbents. In the last part of this review, the novel prospects in the regeneration of the biochar are presented in order to achieve a clean technology for alleviating the water pollution challenge.

The Production of Sustainable Concrete with the Use of Alternative Aggregates: A Review

The concrete industry is a core element of the building sector, but it has to deal with the increasing attention on the environmental issues related to the production process: increasing energy efficiency and the adoption of alternative fuels or raw materials represent the most relevant solutions. The present work analyses physical, mechanical, and environmental performances of concrete incorporating residues derived from four main sources (construction and demolition waste, residues from waste treatment, metallurgical industry by-products, and others), as substitutes of either fine or coarse aggregates. Fine aggregates showed the highest number of alternatives and replacement level, with the relevant impact on concrete properties; coarse aggregates, however, always reach a complete replacement, with the exclusion of glass that highly affects the mechanical performance. Construction and metallurgical industry categories are the main sources of alternative materials for both the components, with ceramic and lead slag reaching a full replacement for fine and coarse aggregates.

Self-Nanoemulsifying Drug Delivery Systems (SNEDDS) Containing Rice Bran Oil for Enhanced Fenofibrate Oral Delivery: In Vitro Digestion, Ex Vivo Permeability, and In Vivo Bioavailability Studies

Lipid-based drug delivery systems (LbDDS), such as self-nanoemulsifying drug delivery systems (SNEDDS), constitute a prominent formulation approach for enhancing the aqueous solubility and oral bioavailability of poorly water-soluble compounds. Utilization of biorefinery wastes, such as oil from rice bran, may prove advantageous to both improving drug solubilization and absorption and to achieving sustainable agri-food waste valorization. Here, we assessed the effect of four SNEDDS compositions differing in the oil (rice bran oil and corn oil) and surfactant type (Kolliphor RH40 and EL) on the oral bioavailability of fenofibrate, a BCS class II compound. Prior to the in vivo oral administration of the SNEDDS in rats, drug solubilization was tested in vitro using the static digestion model, followed by the ex vivo permeability study of the predigested SNEDDS using the non-everted gut sac model. No significant variation was observed in the solubilization capacity within the different SNEDDS formulations. On the other hand, the ex vivo permeability data of the predigested SNEDDS correlated well with the in vivo bioavailability data designating the superiority of rice bran oil with Kolliphor EL as the surfactant, to enhance the oral absorption of fenofibrate. Results indicated that valorization of agro-industrial waste such as rice bran oil may prove useful in enhancing the oral performance of LbDDS in the case of fenofibrate, while at the same time maximizing the use of agricultural by-products via the creation of new sustainable value chains in the pharmaceutical field.

Adsorption of Fluorides in Drinking Water by Palm Residues

Fluorides represent a significant problem in low- and middle-income countries (LMICs). In fact, this ion is essential for human health but, if taken in excess, it can cause dental and skeletal fluorosis. In LMICs, the pollution of groundwater from fluorides is of natural origin. Therefore, if providing alternative sources for drinking water (DW) supply is not possible, the use of specific processes for the removal of fluorides becomes essential. The adsorption on alternative materials, such as agro-food residues, can be a valid treatment for the removal of fluorides in the LMIC considering: (i) their optimal removal yields, (ii) the high availability, and (iii) the low cost. In recent years, the interest on the use of palm residues (PRs) becomes significant. Optimal pH, temperature, adsorbent dosage, and possible combination with metals to increase adsorption performances were deeply investigated. The activated PRs also present two other advantages: (i) very high surface area, and (ii) very low reduction in uptake capacity when regenerated. However, all tests were conducted with synthetic waters in laboratory-scale reactors while application on real-scale are absent. This makes other studies on this type of alternative adsorbent material still necessary.

Horizontal Flow Constructed Wetland for Greywater Treatment and Reuse: An Experimental Case

In the coming years, water stress is destined to worsen considering that the consumption of water is expected to increase significantly, and climate change is expected to become more evident. Greywater (GW) has been studied as an alternative water source in arid and semiarid zones. Although there is no single optimal solution in order to treat GW, constructed wetlands proved to be effective. In this paper, the results of the treatment of a real GW by a horizontal flow constructed wetland (HFCW) for more than four months are shown. In the preliminary laboratory-scale plant, Phragmites australis, Carex oshimensis and Cyperus papyrus were tested separately and showed very similar results. In the second phase, pilot-scale tests were conducted to confirm the performance at a larger scale and evaluate the influence of hydraulic retention time, obtaining very high removal yields on turbidity (>92%), total suspended solids (TSS) (>85%), chemical oxygen demand (COD) (>89%), and five-day biological oxygen demand (BOD₅) (>88%). Based on the results of the pilot-scale HFCW, a comparison with international recommendations by World Health Organization and European Union is discussed.